Nobiletin Relaxes Isolated Mesenteric Arteries by Activating the Endothelial Ca²⁺-eNOS Pathway in Rats

Abstract

Aims: Nobiletin, a natural polymethoxylated flavonoid compound, has various beneficial properties, such as anticancer, anti-inflammatory, and antioxidant effects, and it also improves memory. Therefore, we investigated the effects and mechanisms of nobiletin on rat isolated mesenteric arteries (MAs). Methods: We examined vasodilation induced by nobiletin on rat isolated MA rings with a tension study, the expression and activity of endothelial nitric oxide synthase (eNOS) with Western blotting, NO production with DAF- FMDA fluorescence, and intracellular Ca²⁺ concentration ([Ca²⁺]i) with Fluo-3AM. Results and Conclusion: Our study showed that nobiletin elicited a dose-dependent vasodilation in phenylephrine precontracted MA rings, but it did not elicit the same response in pulmonary artery rings. Vasodilation was related to endothelium and activated partly by eNOS. Vasodilation was inhibited by denudation of the endothelium or inhibition of eNOS activity. Nobiletin increased NO production by promoting the phosphorylation of eNOS at Ser-1177 without changing the level of eNOS expression in rat mesenteric artery endothelial cells (RMAECs). Nobiletin increased the concentration of endothelial [Ca²⁺]i, which enhances eNOS activity in RMAECs. In summary, vasodilation induced by nobiletin was dependent on the endothelium and partly on eNOS activation, which is mediated by high endothelial [Ca²⁺]i. Results suggest nobiletin may offer a therapeutic benefit and could potentially be used as a vasodilator for the treatment of hypertension.

Nobiletin Protects Endothelial Cell Function via Upregulation of eNOS/ET-1 and Antioxidant Status-Related Genes under Nonstimulated and Inflammatory Conditions

“…Consistent with these results, nobiletin significantly increased the relaxation of phenylephrine-induced contraction in endothelium-intact rat aorta [33]. In support of this observation, nobiletin has been shown to promote the phosphorylation of eNOS at position Ser-1177 by increasing endothelial [Ca 2+ ]i, thereby increasing NO production and vasodilation in phenylephrineprecontracted mesenteric arteries isolated from rats [34]. In keeping with these findings, nobiletin alleviated iron overload damage in vascular endothelium through increasing eNOS phosphorylation and NO production [35].…”

Co-Existence of Hypertensive and Anti-Hypertensive Constituents, Synephrine, and Nobiletin in Citrus unshiu Peel

“…Ikemura et al [26] also provided a clue for anti-hypertensive effects of nobiletin by feeding experiments in SHR rats, but the results were largely observational lacking in mechanistic explanation. Recently, Yang et al reported that nobiletin exhibits relaxation in mesenteric arteries through the calcium-eNOS pathway in endothelium [32]. However, the anti-contractile effect of nobiletin against vasoconstriction has not been reported, to the best of our knowledge.…”